I use chicken wire cut to fit the pot, with an opening in the center for the plant. I turn the sharp edges down and poke them into the soil. You can use moss or rocks or some other decorations to hide the wire. I have also used 2-3 inch river rocks laid in a single layer on top of the soil, they are too heavy for the cat to move around.
My Russian Blue LOVES to dig, not to do his business, but just for the fun. I once caught him in a bag of potting soil having the time of his life, only his long silver tail was visible outside the bag. :laughing: